Voltammetric characterization of an iridium oxide-based system:: the pseudocapacitive nature of the Ir0.3Mn0.7O2 electrode

Mixtures of IrO2 + MnO2 (30:70 mol%) have been electrochemically studied by cyclic voltarnmetry (CV) in acid solution. The crystalline structure, morphology and the electrochemical properties of the electrodes have been studied as a function of the annealing temperature. X-ray diffraction analysis (XRD), show absence of Mn2O3 phase formation and suggest the possible of formation of a solid solution of IrO2 and MnO2 mainly between 400 and 450 degreesC. The voltammetric behavior depends on the potential cycle number and annealing temperature employed in the preparation of the oxide layer. A good potential window in aqueous H2SO4 and high electroactive area are obtained due to the contribution of Ir redox transitions. Energy-dispersive X-ray (EDX) and scanning electron microscopy (SEM) analysis suggest an enrichment of the Ir content on the surface at the cost of the dissolution of the manganese present in the film when the electrode is submitted to the continuous potential scan. The electrodes have been found to perform well in electrochemical capacitor applications with a specific capacitance close to 550 F g(-1). The large capacitance exhibited by this system arises from a combination of the double-layer capacitance and pseudocapacitance associated with surface redox-type reactions. (C) 2002 Elsevier Science Ltd. All rights reserved.